The invention relates to a charge pump configuration for matching a charge pump to the prevailing conditions. The charge pump configuration has a charge pump which, in order to generate a charge pump current, has a plurality of interconnected pump stages with at least one respective pump capacitor.
It is a widely known fact, which requires no further explanation, that particular applications in integrated semiconductor circuits frequently require a voltage that is different than the supply voltage. So long as the magnitude of the voltage that is to be generated is smaller than the supply voltage applied to the integrated semiconductor circuit in question, this can still be achieved using relatively simple devices. The situation is different, however, if the magnitude of the voltage that is to be generated in the integrated semiconductor circuit is larger than the corresponding supply voltage. Particularly in integrated semiconductor memories, such as a flash memory, an EEPROM, a DRAM or an FRAM etc., very high positive and also negative voltages are required from time to time during operation. At the same time, however, the constant development toward smaller and smaller semiconductor configurations require a continuous reduction in supply voltage. Thus, in order to be able to produce relatively high voltages efficiently and also with the aforementioned low supply voltages, special pump technology is required.
For this, use is generally made of charge pumps having a plurality of pump stages which operate on the basis of the principle of capacitive voltage multiplication and, in the simplest case, have one MOS diode and one capacitor per pump stage.
A generic charge pump having a multiplicity of pump stages is described in Published, European Patent Application EP 0 865 149 A2 (corresponding to U.S. Pat. No. 6,046,625). A charge pump, known from EP 0 865 149 A2, has multiple pump stages for step-by-step charge transfer from a power supply on one side, which outputs the supply voltage, to a load capacitor on the other side of the charge pump, at which the increased voltage can be tapped off. Charge is transported to the load capacitor via a plurality of diodes and pump capacitors, which are a component part of the individual pump stages and together form the power path. In this context, the diodes are alternately turned on and off, and the pump capacitors are alternately charged and discharged.
For such a charge pump, the following is generally true in the steady, that is to say a settled state:
VL=nxc2x7VDD+VINxe2x88x92nxc2x7IL/fxc2x7C,
where VL and IL denote an output potential and an output current, respectively, of the charge pump, n denotes the number of pump stages, VDD denotes the supply potential, VIN denotes the input potential, C=C1+C2+. . . + Cn denotes the total capacitance and f denotes the frequency of the charge pump configuration. In this case, nxe2x89xa6nworst case is a flexible variable and fundamentally determines an efficiency xcex7 of the charge pump, where xcex7=PL/Pin corresponds to a ratio of a power output from the charge pump to the input power. In this context, nworst case denotes the minimum number of pump stages in the charge pump configuration which needs to be provided in order to configure the charge pump configuration for all conceivable permutations of input and output voltages/currents.
In the aforementioned charge pump, the number of pump stages and hence of pump capacitors n first needs to be configured for the worst case, that is to say for a minimal supply potential and input potential and a maximum output potential/current required. Since the worst case generally arises very rarely, the charge pump typically has too high a rating for normal operation, which results in poor efficiency. Therefore, the charge pump consumes much more power than is actually required.
Since the aforementioned charge pumps are also increasingly used in contactless electrical and electronic systems, for example mobile phones, chip cards, smart cards or wireless devices used in medicine, in which the power is generally supplied by a battery or a storage battery and is thus limited, an additional requirement here is for the total power consumption of the system to be kept as low as possible in order to permit a long operating life. Charge pump configurations based on the prior art meet this demand only to a limited extent or not at all, however.
It is accordingly an object of the invention to provide a charge pump configuration that overcomes the above-mentioned disadvantages of the prior art devices of this general type, which can be matched to the prevailing conditions as best as possible in terms of its efficiency.
With the foregoing and other objects in view there is provided, in accordance with the invention, a charge pump configuration. The charge pump configuration includes a charge pump for generating a charge pump current and has a plurality of interconnected pump stages each with at least one pump capacitor. A device is connected to the charge pump and is used to turn off at least one of the interconnected pump stages on a basis of prevailing conditions that need to be taken into account.
Accordingly, the charge pump configuration is provided which is characterized in that a device is provided which can be used to bridge or turn off at least one of the pump stages on the basis of the conditions which need to be taken into account.
The pump stages needed by the charge pump configuration are optimally chosen for the present operating point on the basis of input and output voltages and currents, which allows the efficiency of the charge pump configuration to be set in an optimum fashion. In this case, the charge pump is shortened by an appropriate number of pump stages. The shortening of the charge pump is effected very simply by bridging or by disconnecting pump stages that are not required. In this context, the output current or output voltage of the charge pump can be measured and evaluated by a measuring device. On the basis of the output current or output voltage, a regulating signal is then produced which is fed back to the charge pump as a controlled variable. The regulating signal can be used to disconnect or bridge one or more pump stages which are typically not required.
Alternatively, it would also be conceivable to provide a desired output current or a desired output voltage from the charge pump by a suitable selection of the number of pump stages. In this way, the charge pump configuration having different output currents or output voltages can be produced in a defined manner, according to application.
In the simplest embodiment, pump stages which are not required can be disconnected or bridged by an A/D converter which uses the analog output signal from the charge pump to produce a digitized output signal which is supplied to a downstream-connected up/down counter or to a shift register. The shift register or up/down counter produces a digital regulating signal from the digitized output signal. In the simplest case, the digital regulating signal can be used as an enable signal for driving the individual pump stages, in order to turn them off.
The simplest way of shortening the charge pump configuration is from the beginning of the pump, that is to say from the input of the charge pump, but in principle the configuration can be shortened at any point of the charge pump.
The principle of shortening the charge pump is particularly advantageous with all forms of positive and also negative pumps. Charge pumps with feedback become useful only when shortened in accordance with the invention.
It is particularly advantageous, as is yet to be described in detail for the charge pump configuration below, if each of the pump stages can be disconnected or bridged individually and independently of each of the other pump stages. In practice, however, it is entirely sufficient if a few pump stagesxe2x80x94typically one or twoxe2x80x94are disconnected by suitable circuit measures, as the present invention has made possible.
It is particularly advantageous if the pump capacitors in one or more bridged or turned-off pump stages are at the same time used for buffering the output voltage.
Typically, all the pump capacitors have the same respective capacitance.
The controllable switches can advantageously be in the form of simple transistor elements, for example in the form of MOS transistors, or else in the form of diode elements, in particular in the form of MOS diodes. Naturally, the controllable switches can also take any other form.
Advantageously, the control connection of the controllable switches is connected to a boost capacitor and to a boost transistor such that, at the instant of a flow of charge through this controllable switch, the conductivity thereof is increased. Particularly in the case of controllable switches which are configured for high-voltage applications or high-current applications, this measure is absolutely essential in order to be able to provide a charge pump having a sufficiently high clock frequency.
In accordance with an added feature of the invention, the device is a closed-loop control device.
In accordance with an additional feature of the invention, the device has a measuring device connected to and recording the charge pump current and/or an output potential of the charge pump. An evaluation device is connected downstream of the measuring device and generates a regulating signal in dependence on the charge pump current and/or the output potential. The evaluation device is connected to the charge pump and the regulating signal is fed back to the charge pump as a controlled variable.
In accordance with another feature of the invention, the device has an analog-to-digital (A/D) converter connected to the charge pump and uses at least one of the charge pump current and an output potential to generate a digitized output signal. An evaluation device being either a shift register or an up/down counter is connected downstream of the A/D converter and receives the digitized output signal. The evaluation device has an output and generates at least one enable signal as a regulating signal available at the output.
In accordance with another feature of the invention, each of the interconnected pump stages has a respective switching device connected to the evaluation device and receives and is controlled by the enable signal. Each of the interconnected pump stages is able to be turned off individually by the switching device respectively associated therewith.
In accordance with another added feature of the invention, the charge pump has an input, and the evaluation device is disposed such that the interconnected pump stages which are not needed are initially turned off from the input of the charge pump.
In accordance with another additional feature of the invention, at least one of the interconnected pump stages that is turned off buffers a supply potential.
In accordance with another further feature of the invention, the charge pump includes an input for receiving an input signal; a capacitor connection for receiving a respective supply potential and is connected to the pump capacitor of each of the interconnect pump stages for precharging the pump capacitor; and an output for providing an output signal. The interconnected pump stages are connected between the input and the output, the interconnected pump stages each have at least one controllable switch. A control circuit is connected to and drives the controllable switch of each of the interconnected pump stages. A clock generator circuit generates a clock signal for driving at least one of the pump capacitor and the control circuit. A buffer capacitor is connected to the output of the charge pump.
In accordance with an added feature of the invention, the controllable switch is a transistor element, in particular a MOS transistor.
In accordance with an additional feature of the invention, the controllable switch is a diode, in particular a MOS diode.
In accordance with another feature of the invention, the pump capacitor of each of the interconnected pump stages each have an equivalent capacitance.
In accordance with a further feature of the invention, the evaluation device and/or the measuring device is a program-controlled unit.
In accordance with a further added feature of the invention, the device has at least one controllable switching device driven by an enable signal. The controllable switching device has a unit connected to the pump capacitor and is used for applying to the pump capacitor a reference-ground potential in a turned-off state, and a supply potential and a reference-ground potential, alternately, in a turned-on state.
In accordance with a further additional feature of the invention, the controllable switch has a control connection with at least one boost capacitor and at least one boost transistor connected upstream of the boost capacitor such that a conductivity of the controllable switch is increased at an instant of a flow of charge.
In accordance with a concomitant feature of the invention, the pump capacitor feeds back current.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a charge pump configuration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.